You can find out how much memory and VRAM are installed in your Mac by following this procedure:

Click on the Apple icon in the upper left corner of the display. Click on About this Mac, and you will see a popup window with basic information displayed. Your Mac's memory is displayed on this page. Next click More info... The System Profiler will be displayed. In the left pane, there should be listed something like Graphics/Display or PCI/AGP Cards (may vary depending upon your Mac's installed components and age). Click on that and you'll see your display specifications in the right pane. Your video memory will most likely be displayed as VRAM (total).

I suspect that your Mac's video adapter is incompatible with Virtual Villagers video requirements. I have seen the symptoms you're describing on computers that don't support the video modes required by Virtual Villagers.